Question

A sample of helium behaves as an ideal gas as it is heated at constant pressure from 273 K to 388 K. If 80 J of work is done by the gas during this process, what is the mass of the helium sample? The universal gas constant is 8.31451 J/mol · K. Answer in units of g

Answer 1

The mass of the helium gas sample after the work is done by the gas during the process is 0.099 g.

Number of moles of the helium gas

The number of moles of the helium gas is calculated as follows;

W = nRT

where;

• n is the number of moles
• W is the work done
• R is universal gas constant = 8.31451 J/mol · K
• T is the final temperature = 388 K

273 K = 0⁰C and 388 K = 115⁰ C

from 0⁰C to 115⁰C = 115 - 0 = 115⁰ C

115⁰ C = 388 K

The number of moles is calculated as follows;

n = W/RT

$n = \frac{80}{8.315 \times 388} \\\\n = 0.0248 \ mol$.

Mass of the helium sample

Mass of the helium sample is calculated as follows;

m = Mn

where;

• M is the molar mass of helium gas = 4 g/mol

m = 4 g/mol x 0.0248 mol

m = 0.099 g

Thus, the mass of the helium gas sample after the work is done by the gas during the process is 0.099 g.

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